A full duplex communication technique has been discussed as a technique of improving system throughput in an environment where many terminals reside. In full duplex communication, a single terminal simultaneously performs transmission and reception in a predetermined frequency band. The full duplex communication can improve the use efficiency of the time resource in comparison with the conventional half duplex communication. More specifically, an improvement to achieve twice throughput is expected at the maximum.
During full duplex communication, a possible difference in time length between the uplink traffic and downlink traffic causes some problems. For example, during continuation of downlink transmission by one terminal, possible completion of uplink transmission by the other terminal causes a duration only with downlink transmission. The one terminal is required to transmit acknowledgement response (ACK response) SIFS-after completion of uplink transmission by the other terminal, but cannot transmit an ACK response because the downlink transmission continues. To address this, a method of causing the uplink traffic and the downlink traffic to have the same transmission time length and a method of delaying ACK transmission have been proposed. Unfortunately, the length of the ACK frame is not necessarily constant. Accordingly, there is a possibility that timings at which reception of the ACK frame is completed by terminals deviate from each other. Consequently, there is a possibility that a hidden terminal problem or an exposed terminal problem occurs and the start timing of transmitting the next frame cannot be synchronized. Such a problem may degrade the system throughput.